Versatile optical switching for wavelength-division multiplexed system

ABSTRACT

Scalable and modular WDM systems to provide a number of processing functions which include, among others, signal detection, signal monitoring, wavelength conversion, signal regeneration, and generation of new WDM channels. Such WDM systems include a platform with an optical switching network and module slots for engaging WDM modules of different processing functions. Both protocol transparent and opaque WDM modules may be included in such a WDM system to provide versatile applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/575,729, filed Aug. 20, 2000 and issued as U.S. Pat. No. 6,344,912,which claims the benefits of U.S. Provisional Application Ser. Nos.60/207,643, filed May 26, 2000, and 60/209,915 filed Jun. 6, 2000.

BACKGROUND OF INVENTION

This application relates to devices and systems for opticalwavelength-division multiplexed (“WDM”) communication systems, and morespecifically, to devices and systems for processing WDM signals.

An optical WDM system uses a single fiber link to simultaneouslytransmit optical carriers of different wavelengths so that differentchannels of data can be carried by the different carriers and sent overthe optical fiber link at the same time. The optical signal in such afiber link is a WDM signal because it is a combination of differentoptical carriers at different wavelengths. Hence, a WDM system canprovide a broadband transmission and a high transmission speed. DenseWDM (“DWDM”) techniques have been used to increase the number ofmultiplexed wavelengths in a WDM fiber link by reducing the wavelengthspacing between two adjacent wavelengths. In addition, a WDM system canbe made scalable to allow expansion of the transmission capacity bysimply adding the number of optical carriers in the existing fiber linkswithout adding new fiber links.

One of the technical issues of WDM systems is the handling or processingof the WDM signals in a WDM network, including, among others, routing,switching, demultiplexing, multiplexing, adding, dropping, wavelengthconversion, and regenerating. Various techniques have been developed orare under development to address these and other WDM processing issues.Some of these techniques use an “opaque” design in which the optical WDMsignals are first converted into electronic form for electronicprocessing and then are converted back into the optical domain fortransmission. The electronic conversion allows many signal processingoperations to be performed electronically by electronic circuits anddevices, including switching, regenerating, buffering, monitoring thebit error rate, etc.

The opaque systems can use matured and well-established electronictechnologies to provide relatively reliable operations and performance.However, the optical-electronic-optical conversion may increase theoperational latency and require expensive optical-electronic convertingdevices. In particular, such conversion is usually data-format specificand must be designed to meet the requirements of existing protocols anddata bit rates. Hence, although the converting devices can be designedto accommodate multiple existing data formats but it can be difficult,if not impossible, to adapt the converting devices to new data formatsemerged in the future.

One alternative to the opaque design is a “transparent” design where nooptical-to-electronic conversion is performed and an optical signal isdirectly routed or switched in the optical domain. Many conventionaltransparent systems passively direct each optical carrier at a specificwavelength to a fixed port or a desired port according to a commandwithout changing the properties of the carrier such as the carrierwavelength and the data format embedded therein. Hence, such transparentsystems are “transparent” to the protocols and data bit rates ofdifferent signals in different optical carriers. In addition, complexand expensive optical-electronic-optical converting devices can beeliminated to reduce the system cost, physical size, and powerrequirements.

SUMMARY OF INVENTION

The present disclosure includes hybrid opto-electronic WDM processingsystems that combine features of both the opaque and transparent designsto provide scalable and versatile WDM processing capabilities. Thescalability of such hybrid systems allows processing of WDM signals withvariable numbers of multiplexed channels of different wavelengths andpermits receiving and processing of a variable number of WDM signals,i.e., input WDM fibers. The processing functions include, among others,signal detection, signal monitoring, wavelength conversion, signalregeneration, and generation of new WDM channels. The versatile aspectof such hybrid systems allows system reconfiguration to meet differentexisting application requirements and adaptability to future updates andnew application requirements. A reconfigurable modular WDM architectureis disclosed to achieve desired scalability and versatility for theevolving optical WDM fiber communications.

A WDM processing system according to one embodiment may include anoptical switching fabric with an array of optical switching elements anda plurality of module slots surrounding the switching fabric forengaging removable processing modules to optically communicate with theswitching fabric. Each removable module includes a plurality ofreceiving or transmitting ports that are optically linked to therespective switching elements in the switching fabric when engaged in arespective module slot. This WDM processing system is scalable becausethe number of inputs of each input module or the number of outputs ofeach output module can be expanded up to a maximum number set by thedesign of the switching fabric.

In one implementation, an input demux module, an output mux module, alaser module with an array of lasers of different wavelengths, and adetector array with an array of photodetectors are engaged to selectedmodule slots. Each of the lasers may be driven by a respective outputsignal from a photodetector to convert a WDM wavelength or to regeneratea signal at the same wavelength. In addition, each laser may be drivenby a control signal to produce a new signal with a new channel of dataat a desired WDM wavelength.

In another implementation, one or more arrays of semiconductor opticalamplifiers may be placed in one or more module slots. Each semiconductoroptical amplifier may be designed to use the semiconductor gain mediumto optically produce an optical signal. Such an optical signal may be ata WDM wavelength different from an input WDM wavelength when thewavelength conversion is desired, or an amplified version of an inputoptical signal when the regeneration is desired, or a new optical signalat a desired WDM wavelength in response to an electronic signal thatdrives the semiconductor medium. Such a semiconductor optical amplifiermay substitute a laser for the wavelength conversion, signalregeneration, or generation of a new signal without converting an inputoptical signal into an electronic signal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows one embodiment of a modular WDM processing system accordingto one embodiment.

FIGS. 2 and 3 show exemplary implementations of modular WDM systemsusing three diagonal switching arrays based on the design in FIG. 1.

FIGS. 4 and 5 show two exemplary implementations of modular WDM systemsusing a switching fabric formed of non-blocking optical switches.

FIG. 6 shows one embodiment of a modular WDM system which combines ablocking switching fabric with a non-block switching fabric.

FIGS. 7A and 7B show two exemplary embodiments of an optical wavelengthconversion module based on optical gating in semiconductor opticalamplifiers.

FIGS. 8A and 8B show two examples to use WDM channels to drive an arrayof lasers in a laser module for the wavelength conversion and signalregeneration.

FIG. 9 illustrates some functionalities in a modular WDM systemaccording to one embodiment.

FIGS. 10 and 11 show two exemplary applications based on modular WDMprocessing systems.

DETAILED DESCRIPTION

1025182108FIG1025182108BXABing Ai1025182108ArchitectureconsiderationsHybridopaque (electronic) and transparent opticalswitching/routingScalable channels in each fiber,modulesVersatile-modules, flexible arrangement. 1 shows one embodimentof a hybrid WDM processing system 100 with a scalable and versatilemodular architecture. The WDM processing system 100 includes a supportplatform 101 on which other components and devices are mounted orintegrated. An optical switching fabric 110 with a network of opticalswitching elements (e.g., switches 111S, 112S, and 113S) is located onthe platform 101. The switching elements can be individuallycontrollable in response to control commands or signals to switch orroute optical beams in the free space from one side of the switchingfabric 110 to another. The control signals for the switching fabric 110may be generated by a control circuit 140 on the platform 101. A servocontrol mechanism may be implemented in each switching element toactively monitor and correct the errors in switching an optical beam.Each switching element is optical and may be set into either a switchingmode in which a beam is redirected to a desired direction, or anon-switching mode in which a beam passes through without changing itsdirection. The switching mode may include one or more switching statescorresponding to one or more switching directions.

Module slots, e.g., 120 through 127, are formed on the platform 101around and adjacent to different sides of the switching fabric 110. Eachmodule slot is designed to include an engaging mechanism that removablyengages a WDM module to the platform 101 to optically communicate withthe switching fabric 110. Hence, each module slot may be used to engagedifferent WDM modules if needed or be left empty without a WDM module. AWDM module, once placed in a module slot, can optically communicate withthe switching fabric 110 to either transmit optical beams to or receiveoptical beams from the switching fabric 110. One optical beam from oneWDM module engaged in one module slot can be directed by the switchingfabric 110 to another WDM module engaged in another module slot at adifferent location.

Various WDM modules may be designed to perform a number of processingfunctions. The following are examples of some WDM modules.

1. An input fiber module may include an input port to receive an inputfiber and a WDM demultiplexer to have an array of output ports arrangedto optically communicate with different switching elements in theswitching fabric 110. The WDM demultiplexer separates differentwavelength channels from the input fiber into the different outputports.

2. An output fiber module includes an array of input ports to receiveoptical beams for different channels from the switching fabrics 110 anda WDM multiplexer to combine the channels into an output fiber.

3. A detector module may include an array of photosensors to receivebeams of different channels and convert the channel signals intoelectronic signals for, e.g., electronic processing, signal monitoring,wavelength conversion, or signal regeneration.

4. An add or drop channel module may include an array of fibersoptically coupled to the switching fabric 110 to optically add or dropone or more channels. The same drop channel module may operate to dropchannels for one portion of a WDM system and to add channels for anotherportion of the WDM system (see, e.g., the add/drop module 610 in FIG. 6,infra.).

5. A laser module may include an array of lasers to produce laser beamsof different WDM wavelengths for the WDM operation. The laser module maybe used to regenerate one or more particular channels at the same WDMwavelengths to restore the signals, or to generate a WDM wavelength tocarry the data originally carried at a different WDM to avoidcontention. In addition, the laser module may generate one or more newchannels to operate as an add channel module.

6. The WDM modules may also include a wave locker module with an arrayof wavelength sensitive sensors to detect the frequency stability of thebeams from the laser module and to produce control signals to stabilizethe lasers. This module may be integrated within the laser module.

7. An optical-to-electrical interface module may be included to use theoptical WDM channels to drive the laser module for signal regenerationor wavelength conversion. A switching mechanism may be included torearrange the sequence of the received WDM channels so that a WDMchannel can be used to drive a desired laser at a particular WDMwavelength in the laser module (see, e.g., FIGS. 8A and 8B, infra.).

8. An optical wavelength converter may also be used as a WDM module tooptically convert a channel at one WDM wavelength to a channel at adifferent WDM wavelength. One optical mechanism for optical convertersinjects both the modulated signal beam at the WDM wavelength and aunmodulated probe beam at the different WDM wavelength into an opticalmedium. The medium responds to the modulation in the signal beam toproduce the same modulation on the probe beam so that that the outputprobe beam copies the data on the signal beam. Semiconductor opticalamplifiers can be used to construct such optical converters based oneither cross-gain modulation or cross-phase modulation. Nonlinear wavemixing can also be used. See, Ramaswami and Sivarajan, Chapter 3 in“Optical Networks: A Practical Perspective,” Academic Press, San Diego(1998). One advantage of such an optical wavelength converter is itsindependence with respect to protocols and data formats.

The above cross-gain or cross-phase modulation in a semiconductoroptical amplifier can also be used to construct an optical signalregenerator or adder. The optical signal regenerator uses the modulatedinput signal beam and another unmodulated probe beam at the same WDMwavelength to overlap within the semiconductor medium. The signal beamis amplified by transferring energy from the probe beam to the signalbeam. The optical signal adder is a semiconductor amplifier where thegain of the semiconductor medium is electronically modulated so that anew data channel is impressed onto an input optical beam. Therefore,such optical cross-gain or cross-phase devices can be used to replacethe lasers for regeneration, generation, and wavelength conversion whentransparency to protocols and data formats is desirable.

These modules represent only examples of WDM modules and it iscontemplated that WDM modules with above or other functions or somecombinations of functions may also be used. The control circuit 140 mayperform certain processing and control operations for WDM modules inaddition to controlling of the switching fabric 110.

An optical collimating array may be located between a module slot andthe switching fabric 110 to ensure each optical beam is collimated andthus to maintain a desired optical coupling efficiency. The system 100is shown to place such an optical collimating array (e.g., 130 through137) between each module slot and the switching fabric 110. Each opticalcollimating array generally includes an array of collimating opticalelements (e.g., 130A) that are arranged in alignment with a set ofrespective switching elements in the switching fabric 110 for thatmodule slot. Alternatively, optical collimating arrays may be placedonly between selected module slots and the switching fabric 110.

Notably, the switching fabric 110 is all optical in the sense that anoptical beam is optically directed to a desired destination withoutoptical-electronic-optical conversion by the switching elements. Hence,optical beams of various wavelengths can be switched and routed by theswitching fabric 110 no matter what their data formats are. Theaforementioned all optical wavelength converter is also a transparentWDM module. This feature provides the transparency and fast operationsto the hybrid WDM system 100.

In addition, the WDM system 100 also includes “opaque” electrical WDMmodules such as a detector module that converts the optical signals intoelectronic data for processing or monitoring purposes or a laser modulethat generates one or more beams for regenerating a channel signal oradding a new channel signal. Such electrical modules are format specificand must be designed to operate in compliance with one or more specificprotocols or data formats. The combination of the laser module anddetector module can make the WDM system 100 more versatile and adaptableto the requirements of various WDM applications.

For example, the switching fabric 110 can be controlled to direct one ormore optical channels to the detector module to monitor the signalquality or other signal characteristics of such channels. If the biterror rate for a particular optical channel is higher than an acceptablelevel, the control circuit 140 may command the laser module toregenerate that channel before it is sent out to ensure the fidelity ofthe data transmitted in that channel.

For another example, if the WDM system 100 has two module slots toreceive WDM signals from two input fibers, a contention problem canarise when two different channels of data from the two input fibers arecarried by input optical beams of identical or similar wavelengths andthe application requires to send both channels out in a single outputfiber by wavelength division multiplexing. In addition to using theoptical wavelength converter module, the present WDM system 100 canovercome this conflict in wavelength by commanding the laser module togenerate a new laser beam at a different wavelength to carry one of thetwo conflicting channels.

The hybrid, modular WDM system 100 is also adaptive to technical changesand modifications or developments in industrial standards. Each WDMmodule can be modified or replaced as needed without affecting othermodules. For example, if a new WDM data protocol or data format isadopted in the environment in which the WDM system 100 operates, a WDMmodule whose operation is affected by the protocol or data format, suchas the laser module or the detector module, can be replaced by a new WDMmodule in compliance with that protocol or format, without changing theother portion (e.g., other WDM modules) of the WDM system 100. Hence,different from many conventional WDM processing systems, the presenthybrid WDM modular design allows a system to “evolve” with newdevelopments in the WDM technology.

The number of the switching elements in the switching fabric 110determines the maximum number of WDM channels that can be simultaneouslyprocessed in the WDM system 100. Each WDM module may only use a portionof the full channel capacity of a module slot and can be modified orreplaced to add additional channels when needed. For example, assumingthe switching fabric 110 can process up to 124 channels, each moduleslot then has a full channel capacity of 124 channels. A WDM lasermodule, however, may have only an array of 8 lasers to produce 8 laserbeams of different wavelengths for a particular application, leaving theremaining 116 positions empty. When the WDM system 100 requires 32 or 64channels, additional lasers may be added to the laser module or a newlaser module with 32 or 64 lasers may be used to replace the 8-lasermodule. This example illustrates the advantage of the scalability of thepresent modular architecture of the WDM system 100.

In general, the applicable WDM modules mounted on the platform 101 for aspecific WDM application may be arranged on the available module slotsin accordance with the configuration of the switching fabric 110 and theavailable switching states of the switching elements in the switchingfabric 110. This is because a receiving WDM module, such as a detectormodule or a channel MUX module, must be positioned relative to theswitching fabric 110 in a properly situated module slot to receive theproper optical beams of different wavelengths. The following describestwo exemplary types of switching fabric 110: the blocking switchingfabric and non-blocking switching fabric.

In a blocking switching fabric, when a switching element is set todirect one beam from a transmitting WDM module to a receiving WDMmodule, the switching element blocks another beam from anothertransmitting WDM module to reach the same receiving WDM module. Thefree-space switching fabrics shown in FIGS. 1, 2, and 3 are blockingwhen each switching element in the switching mode is a reflector. Such areflector switching element may be positioned into a respective opticalpath of one or more transmitting WDM modules to operate in the switchingmode by reflecting one or more beams, or may be positioned out of therespective optical path when operating in the non-switching mode. In theswitching mode, the reflector may have only one orientation so that aninput beam can be only reflected to one fixed direction, or have two ormore orientations so that an input beam can be reflected to two or morefixed directions.

As illustrated, a diagonal switching array of 2×2 optical switchingelements is used as the building block for the switching fabric 110. Theswitching fabric 110 may include one or more such diagonal switchingarrays. In FIG. 1, for example, the switching fabric 110 includes threediagonal switching arrays 111, 112, and 113 arranged in a serialconfiguration. In this arrangement, the number N of switching elementsin each diagonal switching array sets the upper limit of the number ofdifferent channels in a WDM input that can be processed simultaneously.The numbers of WDM inputs and outputs are not so limited if the numberof channels does not exceed N. More WDM inputs and outputs can beaccommodated by simply adding more diagonal switching arrays orincreasing the switching states of the switching elements.

FIG. 2 shows one implementation 200 of a hybrid WDM system using threediagonal switching arrays based on the modular system 100 shown in FIG.1. Each 2×2 switching element is a reflector and has only one switchingstate when the reflective surface is along the diagonal direction in theswitching mode: a beam incident from the left side is reflected downwardby one reflective surface of the reflector and the beam incident fromthe top is reflected rightward by another opposing reflective surface.Hence, the reflector in each switching element prevents the incidentbeam from the left from going to the right. Under such a switchingfabric design, the system 200 uses a laser module in the module slot121, a channel filter demux module 220 in the module slot 122, an addchannel module 270 in the module slot 120, a channel mux module 250 inthe module slot 126, a detector module 240 in the module slot 125, and adrop channel module 230 in the module slot 124. A wave locker module 260may be optionally placed in the module slot 127.

If each 2×2 switching element can have another switching state byrotating the reflector by 90 degrees, an expanded system 300 in FIG. 3may be constructed with a second channel filter demux module 310 at themodule slot 123, a second channel mux module 320 at the slot 125 bymoving the detector module 240 to the slot 127 across the laser module210. Note that with proper controls of the switches, any input opticalbeam from the add channel module 270, the laser module 210, the twodemux modules 220 and 310, or the second add channel module 320 can bedirected to any of the detector module 240, the mux module 250, and thedrop channel module 230. Additional diagonal switching array can beadded to further increase the number of inputs and outputs.

An alternative design for the switching fabric is a non-blockingapproach. In a non-blocking design, each switching element includes anon-blocking switch to allow any input to reach any output regardlessthe operating mode of the switch. The input signal coupled to each inputport is directed to any of the output ports as desired and all inputsignals are respectively directed to their desired output portsdepending on the control signal to each non-blocking switch. A 2×2non-blocking switch, for example, can switch two inputs to two differentoutputs at the same time.

FIGS. 4 and 5 show two non-blocking type WDM systems based on themodular platform 101 using 3×3 and 4×4 non-blocking switches as theswitching fabric 110, respectively. The switching fabric includesnon-blocking switches that are optically independent to one another andare operable to switch optical signals of different WDM wavelengths. TheWDM modules are divided into light-transmitting modules that transmitlight towards the switching fabric (e.g., a laser module, an add channelmodule, and an input demux module) and light-receiving modules thatreceive light from the switching fabric (e.g., a drop channel module, adetector module, and an output mux module). The number of input oroutput terminals of each non-blocking switch should be equal to orgreater than the greater of light-receiving modules and thelight-transmitting modules. The input terminals of each non-blockingswitch are respectively coupled to the light-transmitting modules andthe output terminals are respectively coupled to the light-receivingmodules.

Each terminal of each non-block switch is uniquely coupled to adesignated channel output of a light-transmitting module or a designatedchannel input of a light-receiving module. Hence, the number ofnon-blocking switches sets the upper limit to the number of WDM channelsthat can be simultaneously processed. The number of input or outputterminals in each switch sets the upper limit to the number oflight-transmitting or light-receiving modules. For example, assuming theswitching fabric includes N non-blocking switches with each having Kinputs and K outputs, both the maximum number of light-trasmittingmodules and the maximum number of light-receiving modules are K. Themaximum number of WDM channels at different WDM wavelengths in eachmodule is N. When only n<N number of WDM channels are received, only nnumber of non-blocking switches are used for switching and the remaining(N-n) non-blocking switches are unused.

In FIG. 4, the three input ports of each 3×3 switch are respectivelyconnected to receive three WDM channels from the add channel module, thelaser channel module, and the input common module, respectively. Itsthree output ports, accordingly, are connected to three assigned inputports for use in the drop channel module, the detector channel module,and the output express module, respectively. Different switches areconnected to different input and output terminals at different WDMwavelengths. An input WDM channel from the input common module, forexample, may be switched to a designated input terminal of the dropchannel module, or the detector channel module, or the output expressmodule.

One embodiment of such a non-blocking K×K switch is a fiber coupledswitch where the K input ports and K output ports are fiber coupled.Thus, unlike the switching fabric shown in FIGS. 1-3, where each switchcommunicates with various signal blocks via free space, the non-blockswitch here communicates with WDM modules by fiber links. In the freespace communication, although collimated, each beam still has a certaindegree of divergence due to its Gaussian beam properties. Hence, it maybe desirable to limit the optical path length to about one Rayleighlength from a terminal where an optical signal is originated, e.g., theadd channel block, to another terminal where the optical signal isreceived, e.g., the output express block. This is to reduce the opticalloss during the switching operation. When the fiber-coupled non-blockingswitches are used, the fiber links relaxes such restriction on theoptical path length. Alternatively, the fiber links may be replaced bywaveguides.

Each non-blocking switch may be implemented with a plurality of opticalswitches to switch inputs to the outputs in the free space internally.Within each switch, the optical length from on input port to anotherinput port may be limited to the Rayleigh range as described above. Aservo loop may be used between each switch and each output port toensure that the beam of a switched signal is approximately centered atthe receiving facet of each output port. A photosensing element may beused at each output port to determine whether a switched beam from aswitch is properly centered at an output port. If not, an error signalmay be generated and is fed back to that switch so that the orientationof the switch is adjusted to center the beam.

Blocking switches and non-blocking switches may be combined to form aswitching fabric for a modular WDM system. FIG. 6 shows one example ofsuch a system 600 formed on the platform 101. The switching fabricincludes a blocking part 111 and a non-blocking part 620. A N dropchannel module 610 is used as an interface to couple the beams from theblocking part 111 in the free space into the fibers of the non-blockingpart 620. The blocking part 111 switches the beams from either the lasermodule 210 or the add channel module 270 to the drop channel module 610.A detector module 630 may be placed in the remaining module slot 127 toreceive beams from the laser module 210 or the add channel module 270.The drop channel module 610 operates as a light-transmitting module forthe non-blocking part 620. In the example of 3×3 non-blocking switchesshown, the other two additional light-transmitting modules may be twodemux modules 330 and 310. The respective three light-receiving modulesmay be the channel mux modules 250, the detector module 240, and thedrop channel module 230. Only connections for one 3×3 non-blockingswitch are shown.

FIG. 7A shows one embodiment of a WDM optical wavelength converter (OWC)based on optical gating in an array of semiconductor optical amplifiers(SOAs). A N×N optical switch 710 has N inputs and N outputs and isoperable to switch an input to any of its outputs in response to acontrol signal 712. The SOAs in the SOA array 720 respectively receive Noutputs from the switch 710. Each SOA also receives a unmodulated inputbeam at a designated WDM wavelength. The interaction between themodulated WDM signal from a respective output of the switch 710 and theSOA causes an intensity modulation on the unmodulated input beam throughcross gain modulation. An optical filter is implemented to filter theoptical output from the SOA to transmit only the designated WDMwavelength for that SOA by blocking the input WDM signal from theoptical switch 710. This filter and other similar filters fortransmitting different WDM wavelengths designated to different SOAs forman optical filter array 730. FIG. 7B shows an alternative embodiment inwhich the filter array 730 is replaced by a WDM multiplexer 740 tocombine the newly-converted WDM channels at different wavelengths toproduce a WDM output 750.

The above OWC may be incorporated into a hybrid WDM system based on theplatform 100. For example, the OWC 600 substitute the second add channel320 in the module slot 125 for the hybrid system 300. In anotherexample, the WDM system shown in FIG. 5 may replace the output expressmodule No. 2 with the OWC. One advantage of such optical wavelengthconversion is its transparency to protocols and data formats. The OWCcan also free up the laser channel module for generating new channels orregenerating channels that are distorted or degraded.

Referring back to the WDM systems shown in FIGS. 2 through 6, the lasermodule 210 with an array of lasers may be operated in a number ofdifferent configurations. As a signal generator/adder to generate one ormore new WDM channels, the laser module 210 is driven by electronicsignals from the control circuit 140 so that electronic data isconverted into optical format for WDM processing or transmission. Whenthe laser module 210 is used to regenerate one or more WDM channels orto convert one or more WDM wavelengths, an electronic or optical switchis used so that an input WDM channel can be associated with a properlaser at a desired WDM wavelength in the laser module 210.

FIGS. 8A and 8B show two different configurations for using input WDMchannels to drive the laser module 210. In FIG. 8A, an N×N opticalswitch 812 and a detector array 820 with N photosensors are used toprovide an optical-to-electrical interface module 801 to drive the lasermodule 210. Different WDM channels are sent into the optical switch 810to produce output WDM channels in a desired sequence. The detector array820 receives the output WDM channels and converts them into electronicsignals as indicated by the dashed lines. The electronic signals arethen used to drive the laser module 210 for either wavelength conversionor signal regeneration. The optical-to-electrical interface module 802in FIG. 8B uses a N×N optical switch 830 in lieu of the optical switch810. The detector module 820 is used to convert the input WDM channelsinto electronic signals that are rearranged by the electronic switch 832if needed. In both configurations, an electronic switching controlsignal (812 or 832) is generated from the control circuit 140 to controlthe operation of the optical or electronic switch. The module 801 or 802may beA hybrid WDM system based on the above and other WDM modulesplugged into the platform 100 in FIG. 1 may have versatile applications.FIG. 9 illustrates some of the functionalities of such a hybrid WDMsystem, including passive optical switching and routing, signal detectorand monitor, wavelength conversion, and optical regeneration andgeneration. In addition, electronic IP processing and routing may alsobe implemented by adding an electronic IP processing module orincorporating the needed circuits and software in the control circuit140. Hence, in addition to processing one or more WDM inputs, the systemcan also process one or more electronic input channels and send outelectronic output channels. An electronic input channel may also beconverted into an optical channel by using the laser module (e.g., 210)and added to a desired WDM signal. Depending on the types of WDM modulesinstalled on the platform 100, the system can be configured to use anyone of or a combination of functions of the WDM modules for a range ofapplications.

For example, when the laser module is installed, the system can functionas a WDM laser transmitter to generate a multi-channel WDM signal.Assume the laser module has an array of 32 lasers and each laser cancarry 10 Gbps of data. The total transmission speed of the WDM signal isthen 320 Gbps. When the detector module is installed, the system canoperate as a WDM receiver to convert individual channels into electronicdata after demultiplexing (e.g., by the demux 220 in FIG. 2). The systemcan also use the input demux to filter an input WDM signal and toperform switching operations without performing the wavelengthconversion or signal regeneration (i.e., protocol independent passiveoperations). When a new optical channel is needed in a fiber link, thesystem can use the laser module to create the new optical channel andadd the channel to the WDM signal. The system can also multiplex two ormore low-rate channels into a high-rate WDM signal or vice versa tomanage the communication traffic.

FIG. 10 shows one exemplary application of the hybrid WDM systems in apoint-to-point fiber communication link. Two hybrid WDM systems are usedas two nodes in the point-to-point link. Each WDM system may receive andtransmit WDM or DWDM signals over the fiber link, or add other signalsin various formats (e.g., IP, ATM, SONET, SDH, PHD, etc.) to the WDMsignal. The receiving WDM system may use the demultiplexing and droppingfunctions to separate signals of different formats.

FIG. 11 shows another exemplary application of the hybrid WDM systems ina local network. The local network includes a feeder network that isconnected to a backbone network and is connected to multiple userdistribution networks. The hybrid WDM systems are included in the accessnodes (ANs) of the feeder network to connect the users in thedistribution networks. The feeder network can be designed based on anumber of network topologies, including the mesh and ringconfigurations. The example shows a double-ring feeder network where twofiber rings in opposite directions are used. Each user distributionnetwork may use the bus configuration, the ring configuration, the starconfiguration, or any other configurations.

This use of the hybrid WDM systems provides the local network withcertain network intelligence and flexibility at the access node level inboth the optical and electronic domains. Data channels in an input WDMsignal can be transmitted through an access node passively without anyoptical or electronic processing if so desired. Alternatively, the datachannels may be manipulated either optically or electronically beforeexiting the node. The optical manipulation may include opticalswitching, adding/dropping, or optical wavelength conversion and theelectronic manipulation may include, electronic IP routing,electronically reshaping and conditioning of the data channels, andregenerating the channels.

The hybrid and modular architecture of the present WDM systems based onthe platform 100 in FIG. 1 allows the original equipment manufacturer tospecifically design a WDM system to meet a customer's specification. Tobuild a customer system, the required WDM modules are specificallydesigned and made to meet the customer specifications. The WDM modulesand associated electronic circuits are then installed on the platform100. Next, the operation of each installed module is tested. Finally, acompleted system that passes all tests is shipped to the customer. Sucha system is designed to include a set of firmware instructions in thecontrol circuit 140 so that the system can operate according to controlroutines and instructions of a customer network management softwarepackage. This allows the customer to change the operation pattern of thesystem by changing certain instructions or routines in the networkmanagement software as needed. Alternatively, a network managementsoftware package for the hardware system may be provided to thecustomer.

The present modular architecture further allows a completed system to bemodified and expanded on the module by module basis. If the requirementsfor one or more modules in the completed system are changed, the systemcan be updated by replacing or modifying certain modules.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications andenhancements may be made without departing from the following claims.

What is claimed is:
 1. A system, comprising: a support platform; anoptical switching network of a plurality of optical switches disposed onsaid platform to redirect one or more optical beams in response tocontrol signals respectively applied to said optical switches; aplurality of module slots located on said platform and distributedaround said optical switching network, each module slot including anengaging mechanism to removably engage a module which either directs oneor more optical beams to said optical switching network or receives oneor more optical beams from said optical switching network; an inputfiber module having an input fiber port to receive awavelength-division-multiplexed (“WDM”) signal formed of a plurality ofoptical carriers of different wavelengths, an array of output ports tooutput said optical carriers separately, and a WDM demultiplexer coupledbetween said input fiber port and said output ports to separate saidoptical carriers into said output ports, respectively, wherein saidinput fiber module is engaged to a first module slot on said platform tocouple said optical carriers respectively output from said output portsto said optical switching network; an output fiber module, engaged to asecond module slot on said platform, having an array of input ports atleast a portion of which respectively receive optical carriers ofdifferent wavelengths from said optical switching network, an outputfiber port, and a WDM multiplexer coupled between said input ports andsaid output fiber port to combine said received optical carriers into anoutput WDM signal in said output fiber port; a laser module engaged to athird module slot on said platform, having an array of lasers to producelaser beams at different wavelengths and arranged to direct said laserbeams to different optical switches in said switching network; and awavelocker module on said platform and operable to detect frequencystability of each laser beam out of said laser module and to produce alaser control signal to each laser in said laser module to stabilizelaser wavelength.
 2. The system as in claim 1, wherein said wavelockermodule is integrated with said laser module.
 3. The system as in claim1, wherein said wavellocker is separate from said laser module and isengaged to a fourth module slot on said platform which is located toallow said wavelocker module to receive said laser beams from said lasermodule through at least a portion of said optical switching network. 4.The system as in claim 1, further comprising a detector module engagedto a designated module slot on said platform and having an array ofphotosensors arranged to receive optical beams from different opticalswitches in said switching network and to produce detector outputsignals indicating information in said optical beams.
 5. The system asin claim 1, further comprising an optical wavelength conversion moduleengaged to a designated module slot on said platform to receive a signalbeam at a first WDM wavelength from said optical switching network and aconversion optical beam at a second WDM wavelength different from saidfirst WDM wavelength, wherein said optical wavelength conversion moduleis responsive to a modulation in said signal beam to transferinformation from said signal beam to said conversion optical beam. 6.The system as in claim 5, wherein said optical wavelength conversionmodule includes at least one semiconductor optical amplifier whichexhibits an optical cross gain between said first and said second WDMwavelengths.
 7. The system as in claim 5, wherein said opticalwavelength conversion module includes at least one semiconductor opticalamplifier which exhibits an optical cross phase modulation between saidfirst and said second WDM wavelengths.
 8. The system as in claim 1,further comprising an optical-to-electrical interface module engaged toa designated module slot on said platform to receive one or more opticalbeams from said optical switching network, said optical-to-electricalinterface module operable to drive one laser in said laser moduleaccording to a received optical beam from said optical switchingnetwork.
 9. The system as in claim 8, wherein said optical-to-electricalinterface module drives said one laser to produce a new laser beam tocarry information from said received optical beam at the same laserwavelength as said received optical beam.
 10. The system as in claim 8,wherein said optical-to-electrical interface module drives said onelaser to produce a new laser beam to carry information from saidreceived optical beam at a laser wavelength different from a wavelengthof said received optical beam.
 11. The system as in claim 1, furthercomprising: an electronic processing circuit on said support platform toreceive at least one input electronic signal; an electronic input porton said support platform to receive said at least one input electronicsignal; and an electronic output port on said support platform to outputan electronic signal from said electronic processing circuit and othercomponents on said platform.
 12. The system as in claim 11, wherein saidelectronic processing circuit includes an electronic routing circuit todirect said at least one input electronic signal to a desired outputchannel in said electronic output port.
 13. The system as in claim 11,wherein said electronic processing circuit includes an electronic signaldetector that processes said at least one input electronic signal toextract information therein.
 14. The system as in claim 13, furthercomprising an optical signal generator coupled to said electronic signaldetector to generate a new optical signal that includes said informationextracted from said at least one input electronic signal, wherein saidnew optical signal is directed to said output fiber module.
 15. Thesystem as in claim 1, wherein at least one of said input and said outputfiber modules is coupled to at least either one or both of a feedernetwork and a user distribution network.
 16. A method, comprising:directing a plurality of optical WDM channels to an optical switchingnetwork; converting at least a first optical WDM channel of said opticalWDM channels into an electronic signal to retrieve data according to afirst data protocol in said first optical WDM channel; and opticallyprocessing at least a second optical WDM channel of said optical WDMchannels to produce a new optical WDM channel with informationassociated with information in said second optical WDM channel, withoutrelying on a second data protocol in said second optical WDM channel andwithout converting said second optical WDM into an electronic signal.17. The method as in claim 16, wherein said optical processing includesusing an optical semiconductor amplifier to optically amplify saidsecond optical WDM channel to produce said new optical WDM channel byusing energy from another optical beam at the same wavelength in saidoptical semiconductor amplifier.
 18. The method as in claim 16, whereinsaid new optical WDM channel has a WDM wavelength different from a WDMwavelength of said second optical WDM channel.
 19. The method as inclaim 16, further comprising: receiving an electronic communicationsignal; extracting information from said electronic communicationsignal; generating a new optical signal having said informationextracted from said electronic communication signal; and directing saidnew optical signal through said optical switching network to a desireddestination.